1. Field of the Invention
The present invention relates to a method and device for switching interfaces in a communication device included in a redundant system.
2. Description of the Related Art
SDH (Synchronous Digital Hierarchy)/SONET (Synchronous Optical NETwork) is widely used as global-standard network interfaces particularly in wide area networks. In recent years, for the purpose of further bringing down costs, there is a move afoot to apply Ethernet™ (hereinafter, referred to as “Ethernet”) to wide area networks. In this case, since there are many occasions when a single communication device must accommodate both SDH/SONET and Ethernet interfaces, a device has also been developed in which a SDH/SONET interface card and an Ethernet interface card can be freely replaced with one another in a single slot.
To apply Ethernet to wide area networks, it is necessary to enhance the functions of monitoring and controlling a network, and work for the standardization thereof is now in progress in ITU-T. Specifically, a frame for monitoring and controlling (Ethernet OAM frame) is defined in an Ethernet frame, causing a wide area network to be monitored and controlled. In this standardization work, in order to improve the reliability of Ethernet, it has been standardized to implement a redundant system of SDH/SONET on Ethernet (see ITU-T Standard G.8031/Y.1342, pp. 15-22). Specifically, a frame for switching control, called ETH-APS, is defined, and control information is exchanged between link-connected opposite devices, whereby bidirectional switching is accomplished.
However, although information carried in the above-mentioned ETH-APS frame is basically and approximately the same as the automatic protection switching (APS) bytes K1 and K2 of SDH/SONET, there is an essential difference between them: a main-signal interface for one of them is of a synchronization type, and that for the other is of a non-synchronization type. Additionally, the APS bytes and ETH-APS frame are also different in bit assignment.
Accordingly, to enable a single device to accommodate both interfaces, a switch control section for SDH/SONET and a switch control section for Ethernet may be provided independently and switched depending on the interface type. In other words, it is necessary to mount both the SDH/SONET switching control section and Ethernet switching control section on a control section, resulting in the device being complicated and expensive.
Moreover, the above-described method only assumes that the network interface sections support the same type of network (i.e., any one of SDH/SONET and Ethernet), and no consideration is given to a redundant system in a case of network interfaces for different types of networks. Accordingly, in the above-described example, a SDH/SONET interface section and an Ethernet interface section, for example, cannot be mounted at the same time.